Phenotypic and genotypic characteristics of Algerian isolates of Phytophthora infestans

Abstract

SUMMARY Late blight is one of the most important biotic constraints to potato production in Algeria. Characterization of Algerian P. infestans isolates collected on potato and tomato during 2007 to 2009 was performed for mating type, metalaxyl sensitivity, virulence on a set of potato R-gene differentials, in vitro mycelial growth on agar medium at five temperatures, aggressiveness on leaflets of four potato cultivars and genotypic diversity with 11 microsatellite loci. All isolates from potato but two were A2 mating type, and most of them overcame all 11 R-specific genes from the international differential host set; all A2 isolates were metalaxyl resistant. The two isolates collected from tomato were A1 and metalaxyl sensitive. The presence of both mating types in P infestans in Algeria raises the possibility of the formation of oospores. Mycelial growth was fastest at 19°C for all the isolates, but A1 isolates from potato and tomato grew significantly faster than A2 isolates at 27°C. No aggressiveness differences were noticed between A1 and A2 isolates, but the relative rankings of the isolates changed according to the cultivar and to the component (lesion area, sporangia production) measured. Cvs. Bintje and Spunta (the dominant cv. in Algeria) were highly susceptible. By contrast, the sporulation of the isolates was relatively low on the moderately susceptible cvs Desiree and Atlas. SSR markers revealed a large genotypic diversity and distinct genetic groups, according to mating types and host plants. Phenotypic and genotypic traits suggest that the A2 Algerian population of P. infestans, collected from potato, could be closely related to Western European populations.